1. J/ and hot nuclear matter effects at SPS energy
J/ suppression in AA collisions
Physics motivations
Review of AA results
Disucssion on CNM extrapolations
Charmonium vs open charm
Preliminary results from NA60
E. Scomparin – INFN (Torino)
First Retequarkonii Workshop, October 25th-28th 2010, Nantes France

2. Basics Charmonia suppression has been proposed, more than 20 years
ago, as a signature for QGP
formation
Sequential suppression of the
resonances is a thermometer of
the temperature reached in the
collisions
T/TC
J/(1S)
c(1P)
’(2S)
Phys.Lett. B178 (1986) 416

3. First came NA38/NA
Quantify suppression studying the J//DY ratio vs L, for various systems
pA at 400/450 GeV  extrapolate to lower energies,
Assume abs J/ (158 GeV) = abs J/ (400/450 GeV)
Normalization (J//DY)pp : phenomenological rescaling
NA38
S-U 200 GeV/nucleon
M.C. Abreu et al., PLB449(1999)128
 cold nuclear matter effects explain the observed suppression
NA50
Pb-Pb 158 GeV/nucleon
B.Alessandro et al.,EPJC39 (2005)335
 anomalous suppression, increasing with centrality
~8% error on the calculated CNM reference

4. ...then enters NA60 In-In collisions at 158 GeV/nucleon
After quality cuts 
NJ/ ~ (no matching)
~ (with muon matching)
Matching
Vertex reconstruction
Zvertex
Beam Tracker sensors
windows
z ~ 200 m along the beam direction
(~ m in the transverse direction)

5. pA data in a slide..... 3) 1) 2) Main results: 158 GeV 158 GeV
For the first time NA60 has collected p-A data (p-Be,Al,Cu,In,W,Pb,U)
at 158 GeV, i.e. the same energy (and rapidity) used for AA collisions
Main results:
158 GeV
free proton pdf
EKS98
158 GeV
free proton pdf
absJ/(158 GeV)= 7.6 ± 0.7 ± 0.6 mb 1) 3)
comparing  values
(pA= ppA) from fixed target experiments:
clear dependence on xF
and beam energy
taking into account antishadowing correction (EKS98)
absJ/(158 GeV)= 9.3 ± 0.7 ± 0.7 mb 2)

6. Building CNM reference from pA data
Use pA results collected at 158 GeV, in the same kinematic
and energy range as AA data
Try to disentangle initial (antishadowing) and final state effects
(absorption in nuclear matter)
In particular, when extrapolating from pA to AA, take into
account that in AA collisions gluon antishadowing affects both
projectile and target
Caveat:
The results on absJ/(158 GeV) are rather accurate
However, they do not have an absolute normalization
 go through J//DY ratio, as in NA50
However
NA60 pA results have a limited high-mass DY statistics
Possible to extract the J//DY ratio integrated over A
Not possible to have (as in NA50) J//DY vs A

7. Building CNM reference from pA data
2/ndf = 1.24 DY
J/,’ DD
Normalize pA cross section ratio to the (J/ /DY) |pA158GeV integrated on all the targets
B J//DY = 30.12.30.4
with 2.9<mDY<4.5 GeV/c2
8% error on normalization
Try to reduce it using SU results
Are SU and pA compatible, for
what concerns nuclear effects ?
The answer is yes
Slopes are compatible within 0.3
Normalizations (after rescaling SU
to 158GeV) are compatible within 1

8. Building CNM reference from pA data
The CNM reference curve is then defined with
normalization obtained from the weighted average of the normalizations of pA and SU data
slope fixed from pA data
Errors on the CNM reference
curve include
~3% due to absolute normalization
~3% on average, slightly dependent on
centrality, due to absJ/ uncertainty (not shown)

9. Initial state effects: pA vs AA
SPS energies: charmonium production probes x-region in the
antishadowing region
The extrapolation of CNM effects from pA to AA must take into
account that in AA collisions the antishadowing affects both the projectile and the target nucleons
Calculate shadowing factors, i.e. the ratio between J/
production cross section per NN collisions in AA and in pp, as
Cross sections computed at LO in the Color Evaporation Model
Ratios should not depend too much on the choice of the
underlying model

10. Antishadowing parameterizations
Gluon fusion and qq annihilation
contributions to cc are considered
c¯c hadroproduction cross section is
given by the sum of two partonic contributions gluon fusion (gg) and quark-antiquark
annihilation (q¯q), convoluted with the parton densities in the colliding hadrons
Nuclear modification on PDF are included using EKS98 and EPS08
(EPS08 choice coincides with maximum antishadowing foreseen in EPS09)
CEM formulas from R. Vogt Phys. Rep 310 (1999) 197

11. Shadowing spatial dependence
Nuclear modifications depend also on the spatial location of the
nucleon inside the nucleus (S.R.Klein, R.Vogt, Phys.Rev.Lett 91(2003)142301)
 important in the study of the centrality dependence of SJ/ (shadowing effects are more important for core nucleons)
Various parametrization of the shadowing dependence on the
nucleon position are considered
EKS98, y=0.5, InIn
L(fm)
SInInJ/(y=0.5)
proportional to the local density (symbols, continuous line)
since, depending on centrality, the halo or the core of the nuclei are involved in a different way
proportional to the length L of nuclear matter crossed by the parton (dashed line)
The two approaches
give similar results

12. Influence of antishadowing on AA
1) The J/ production cross section in pA is given by
final state absorption
(J/abs = 8 mb in this calculation. Results of the shadowing contribution to the reference insensitive to the specific J/abs)
shadowing
2) the absorption curve is obtained fitting pAJ//A with the e-L behaviour and then extrapolated to AA using L scaling, neglecting shadowing (as usually done at SPS energies)
3) the fit is compared to 1/A2 AAJ/ , calculated with the same ingredients
1/A J/
J/ suppr.
even in absence of hot medium effects there is a difference between AA result and pA extrapolation
this suppression is an effect generated by neglecting AA shadowing in the reference determination
y=0.5
L(fm)
Npart

13. Anomalous suppression
In-In 158 GeV (NA60)
Pb-Pb 158 GeV (NA50)
Using the previously defined reference:
Central Pb-Pb:
 anomalously suppressed
In-In:
almost no anomalous
suppression
Ratio measured over expected
B. Alessandro et al., EPJC39 (2005) 335
R. Arnaldi et al., Nucl. Phys. A830 (2009) 345
R.Arnaldi, P. Cortese, E. Scomparin Phys. Rev. C 81 (2009),

14. Comparison SPS vs RHIC
Measured/Expected SPS results are compared with AuAu
PHENIX RAA results normalized to RAA(CNM)
Both Pb-Pb and Au-Au seem to depart from the reference curve at NPart~200
For central collisions more important suppression in Au-Au with respect to Pb-Pb
Effect of higher energy
density at RHIC at
constatnt Npart ?
Systematic errors on the CNM reference are shown for all points
PHENIX results from T. Frawley, workshop on “Quarkonium
In Hot Media:From QCD to Experiment”, Seattle 2009

15. Comparison SPS vs RHIC
Plot results as a function of a the multiplicity of charged particles
The relation between the charged multiplicity and NPart is obtained
AuAu  using PHOBOS data
(Phys.Rev.C (2002)
PbPb  using NA50 data
(Phys.Lett.B (2002) 43-55)
Scaling between
SPS and RHIC !

16. Comparison SPS vs RHIC
Comparison can also be done in terms of  * Bjorken
energy density
Energy density evaluation based on several assumptions, e.g.
 dET/d from WA98 data for SPS  no dET/d for CuCu, so AuAu data at the same Npart are used
Control of relative systematics not straightforward

17. pT–dependence of the J/ suppression
NA60: 158 GeV
pT dependence of the J/ suppression investigated at SPS energies:
strong pT dependence
of RCP
 only the low pT J/ψ are suppressed !
pT (GeV/c)
RCP
0-1.5%
pT (GeV/c)
RCP
33-47%
Similar to the behaviour
observed at RHIC
NA50: 158 GeV

18. J/ pT distributions in NA50/NA60: AA vs pA
Systematic errors
 4% for the NA60
points
 <1% for the NA38
 2% for the NA50
Linear increase of pT2 vs L for p-A and A-A, slope smaller in p-A at 158 GeV
L scaling broken between p-A and A-A
Initial state parton scattering cannot be the only source of
transverse momentum broadening. Final state effects ?
“Control experiment”: pA at 400 GeV: comparison NA60/NA50 is OK

19. ’ suppression in p-A and A-A
’/DY values for nuclear collisions (S-U, In-In, Pb-Pb) in good
relative agreement
Preliminary
450, 400 and 200 GeV points
rescaled to 158 GeV
abs’ for p-A collisions at 158
GeV not available (statistics
per target too low)
Fit of pA 400/450 GeV data
 abs’ =7.3 ± 1.6 mb
Fit of S-U, Pb-Pb data
 abs’ =19.2 ± 2.4 mb
Even if (as for the J/)
abs’(158 GeV)> abs’(400 GeV)
an additional suppression in
A-A wrt p-A is likely to be
present

20. v2 measurements for J/ NA60 acceptance: ~ 0 < ycm < 1
Determination from charged particle tracks as measured in
the vertex tracker
v2 for charged particles h± v2

21. J/ azimuthal anisotropy
Limited statistics (<30000 J/ events) prevents a fine binning in Npart/pT
Define 2 broad centrality classes
peripheral
central
v2 consistent with zero for central events, v2 > 0 (2.3) for peripheral

22. J/ azimuthal anisotropy
Introduce a rough pT binning
Centrality
pt<1GeV/c
pt>1GeV/c
0.5% < σ/σgeo < 28%
0.00±0.03
-0.01±0.03
28% < σ/σgeo < 83%
0.03±0.05
0.11±0.05
In spite of the relatively low statistics,
we see an anisotropy for peripheral
events, concentrated at high pT
Hardly a signal of elliptic flow (charm collective motion), since at SPS
Ncc is low (no recombination)
Difficult to have charm
thermalisation
Effect likely to be connected with anisotropic absorption in QGP/nuclear matter

23. Open charm production in p-A collisions
Open charm shares initial state effects with charmonium
 a measurement of open charm in p-A collisions may help
in understanding J/ suppression
Recent results from SELEX and E866 suggest rather strong
nuclear effects on open charm
E866/NuSea Preliminary
A. Blanco et al. (SELEX), EPJC64(2009) 637
M. Leitch (E866), workshop on “Heavy Quarkonia
Production in Heavy-Ion Collisions”, ECT* 2009

24. Open charm dimuons in p-A: NA60
NA50 tried to evaluate DD production studying the IMR in pA
Large background levels (S/B ~0.05 at m = 1.5 GeV/c2)
NA50 had to impose
a constant DD/DY vs A
(i.e. DD= DY ~1 )
M.C. Abreu et al., EPJC14(2000) 443
NA60 is much better placed, thanks to the muon matching
 S/B is ~60 times more favourable

25. IMR in NA60: pA collisions
Best option: separate DD and DY in the IMR using the offset
information, obtained in the vertex detector
1.120.17
Data
Prompt: 0.08
Charm: 0.16
Fit 2/NDF: 0.6
Prompt
Successfully done for In-In
collisions
(R. Arnaldi et al., EPJC59(2009)607)
In p-A because of the smaller
multiplicity, accuracy on vertex
determination is smaller
Possible solution
Use the ratios /DY from NA50 to fix the DY contribution
(not well constrained in NA60 because of the small statistics)
Fit the IMR as DD+DY, after subtracting the small comb. bckgr.

26. Open charm dimuons in p-A: NA60
Take /DY ratios from EPJC48(2006)329 (NA50) to fix the DY
contribution
Good resolution on the
longitudinal position of the
vertex in the IMR (no problem
in target assignment)
400 GeV DD DY
Results given for the 400 GeV
sample only (at 158 GeV DD
contribution much smaller
than DY)

27. Open charm dimuons in p-A: results
Kinematic range: 3.2<ylab<3.7 (-0.17<ycm<0.33)
Study the ratio /DD (reduce systematic errors)
E. S., Hard Probes 2010 Eilat
Preliminary
Systematic errors
Fit starting point
Track 2
/DY (norm. and J/)
Background normalization
Using the measured J/ value one gets DD = 0.960.03
Anti-shadowing would suggest DD >1

28. ...but the difference we see in data is
Open charm kinematics x2 x2
Calculate the expected  for
DD pairs decaying into muons in the NA60 acceptance (400 GeV protons)
DD (acc.)
pA 400 GeV
(3.2<y<3.7)
J/
pA 400 GeV
(3.2<y<3.7)
21 x1 x1 
Antishadowing for DD should be even
stronger than for the J/ DD
If DD has little final state interactions
its  should be significantly larger than
that of the J/ (initial state energy loss
should be the same)....
J/
EKS98
EPS08
...but the difference we see in data is
rather small xF

29. Conclusions
J/ suppression studies at the SPS: large statistics for both
A-A and p-A collisions
Pb-Pb data exhibit a significant suppression beyond CNM effects
In-In (and S-U) data show almost no anomalous suppression
Comparison between SPS and RHIC results in terms of
anomalous suppression: good (qualitative) agreement in terms
of energy density
Preliminary results from open charm production in pA at the SPS:
J/ more suppressed than DD, but measured DD disagrees
with anti-shadowing expectations

30. New result: J/ cross section in pA
J/ production cross sections for pA data
Preliminary
Banda blu-> errore su sigma e normalizzazione (1 sigma)
Systematic error on (absolute) luminosity estimation quite high
Relative luminosity estimate between 158 and 400 GeV
much better known (~2-3% systematic error)
Normalize NA GeV cross section ratios to NA50 results
158 GeV cross sections constrained by the relative normalization

31. New reference using J/ cross sections
Alternative approach for the normalization of the pA reference
curve based on the pA J/ absolute cross section
To fully profit from this approach, a measurement of the absolute J/
cross section in In-In would be needed. For the moment…
J//DY values are obtained rescaling the DY cross section
measured at 450 GeV by NA50 (not enough statistics at 158 GeV)
Main advantage: no assumption on SU, since it is not used
anymore in the fit
Preliminary
No practical consequence on anomalous J/Ψ suppression
difference with previous CNM reference ~1% well within errors

32. pT spectra: some more data points
Systematic
errors explicitly
quoted, when
available
In the literature, one can find a few more measurements of
pT2 in this energy range (NA3, NA38 at 200 GeV)
These experiments seem to suggest a higher pT2 ( 15%) with respect
to the NA60 points  now checking relative systematics in detail

33. Assuming maximum correlation between the errors on the normalization and sigmaabs

34. absJ/ and normalization
In order to obtain the AA reference curve vs. centrality,
(J/ /DY) |pp158GeV is needed
 obtained extrapolating (J/ /DY) |pA,SU158GeV to A=1 (i.e. L=0)
abs=7.6 mb
abs=4.2 mb
EZDC(GeV)
Moving from the 400/450GeV based reference to the 158GeV based reference, both abs and (J/ /DY) |pp158GeV have changed